1. Field of the Invention
The present invention is concerned with an exposure device and is especially intended for the contact print of circuit patterns on circuit boards, but is also suitable for use, for example, with the multilayer technique, the so-called hybrid technique (gate arrays) and the contact print of other printing copies.
2. Description of the Prior Art
Exposure devices of this type, so-called moving lights, are disclosed by DOS No. 29 25 153. These are housings movable across the exposure field in which is provided a tubular light source above a light passage slit located at the bottom side in the housing.
Exposure devices of the afore-mentioned type are known from DOS No. 33 40 653, especially in connection with a device for the printed circuit board exposure in which a so-called circuit board package is pushed through the device thereby being exposed to the stationary exposure source. According to the non-prior-published U.S. application Ser. No. 813,728 now U.S. Pat. No. 4,666,294 a device is suggested permitting an essentially improved circuit board exposure.
However, a weak point exhibited by the construction and way of operation of the state-of-the-art device resides in the actual exposure cycle in respect of which is provided a surface exposure by suitable means, requiring correspondingly extended exposure times. When providing a plurality of luminescent tubes covering the entire exposure field, a uniform scattering and distribution of the intensity will be required likely to result in substantial losses and a non-uniform irradiaton of the circuit boards. When providing a light source to which a correspondingly high energy is supplied and the light of which is fed to the exposure field, for example, via mirrors, extended exposure times result envolving a slow polymerization of the photoresist. The use of so-called moving lights as taught, for example, by DOS No. 29 25 153, admittedly, is a suitable approach to solving the exposure problem because the required high exposure energy can be charged into one single light tube safeguarding a uniform exposure of all exposure field areas. However, simply adopting such conventional "moving light" exposure means is precluded by the fact that, on the one hand, the high energy supply resulting in an extremely high heat development, would affect copy, resist and printed circuit board thus resulting in an intolerable heat expansion of the materials and, on the other hand, the substantially non-parallel light emittance for a contact print of the current paths generally vrey narrow, on account of the excessive irradiation envolved therewith, with the finite thickness of the photoresist, will not be possible, i.e. virtually, unavoidable transverse connections of the current paths would result which can, of course, not be accepted. For, the photoresist, for an optimum steep "flank" requires a high energy supply within a short period of time. This, under special conditions, will be realizable by a "moving light", for, this way of exposure, eliminates the generally customary vacuum contact between copy and circuit board in favour of a "soft contact".